The present invention relates to alkoxy-functional one-component RTV compositions and more particularly, the present invention relates to alkoxy-functional one-component RTV compositions having novel scavengers therein and which have good self-bonding properties.
Alkoxy-functional one-component RTV compositions have been known for some time, see, for instance, BEERS, U.S. Pat. No. 4,100,129. The compositions of the above patent comprise basically a silanol-terminated diorganopolysiloxane polymer, a polyalkoxy-functional silane cross-linking agent and a titanium chelate catalyst as the condensation catalyst. In addition, these compositions comprise various other additives such as fillers, etc. The compositions of the foregoing U.S. Pat. No. 4,100,129 were commercially practical in that they had a shelf-stability of 1 year or more and a commercially acceptable cure rate after that period of storage. However, there were problems experienced with such compositions from batch to batch and from time to time with respect to such shelf-stability and cure rate; that is, in some batches it was found that the cure rate and shelf-stability was not commercially acceptable. Various attempts were made to solve these problems, which attempts were not altogether successful.
Recently there has been devised an alkoxy-functional one-component RTV silicone rubber composition with improved shelf-stability and cure rate over the compositions of BEERS, U.S. Pat. No. 4,100,129 and other prior art compositions, see, for instance, WHITE, et al, U.S. Pat. No. 4,395,526. This patent application discloses a silanol-terminated diorganopolysiloxane base polymer with optionally, a polyalkoxy cross-linking agent, a condensation catalyst and either a pure scavenger or an integrated cross-linker, scavenger having various functionalities which can be utilized to scavenge unbonded hydroxy groups in the composition. As hypothesized in WHITE, et al, U.S. PAT. No. 4,395,526, it was the presence of unbonded hydroxy groups in the prior alkoxy-functional one-component RTV silicone rubber compositions (hereinafter room temperature vulcanizable shall be referred to as RTV) that resulted in the degradation of shelf-stability and in the cure rate of such compositions.
As pointed out in the WHITE, et al, patent the unbonded hydroxy groups would attack and degrade the alkoxy groups on the terminal silicon atoms of the base diorganopolysiloxane polymer. This resulted in the degradation of the shelf-stability and cure rate of the composition. Accordingly, it was the improvement of WHITE, et al, to include certain scavengers in the composition having certain functional groups which would react with the unbonded hydroxy groups such that they could not attack and degrade the alkoxy groups on the base polymer. Accordingly, the resulting compositions have improved shelf-stability and cure rate. One such composition is to be found, for instance, disclosed in DZIARK, U.S. Pat. No. 4,417,042, which comprises the use of certain silazanes and amino-functional siloxanes as pure scavenging compounds for alkoxy-terminated diorganopolysiloxane polymers. It should be noted that the function of the silazane is purely as a scavenging compound to react with unbonded hydroxy groups in the composition. Such a composition is prepared by reacting the silanol terminated diorganopolysiloxane polymer with a polyalkoxysilane cross-linking agent, such as methyltrimethoxysilane, and then once the end-capped polymer is formed, then the scavenging compound is added thereto. It is also disclosed in that patent application as well as in BEERS, Ser. No. 349,537, now abandoned, and LUCAS, Ser. No. 349,538, both of which were filed Feb. 17, l982, that various adhesion promoters may be added to these compositions to make them self-bonding, that is so that the compositions will bond to various substrates without the use of a primer. All the patents and patent applications referred to in this application are incorporated by reference. However, even with such self-bonding additives in such compositions, it was found that such compositions would not adhere very well to polyacrylate plastics.
One of the main uses of one-component RTV silicone rubber compositions is as sealants and particularly as glazing sealants in the construction industry. Accordingly, it is highly desirable if alkoxy-functional one-component RTV compositions are devised or developed such as those in the foregoing WHITE, et al, and DZIARK that are useful as glazing sealants. It is also necessary to point out that many of the plastic windows in highrise buildings are fabricated out of polyacrylate plastic. Accordingly, it is necessary to produce an alkoxy-functional one-component RTV silicone rubber composition which can be utilized as a glazing sealant for polyacrylate plastic windows without the need to use therewith a primer.
Further, shelf-stable, acyloxy-functional one-component RTV silicone rubber compositions are known as disclosed in SMITH, et al, U.S. Pat. No. 4,308,372. This patent discloses that the shelf-stability of such acyloxy-functional one-component RTV silicone rubber compositions is improved by pre-reacting the adhesion promoter with the acyloxy-functional cross-linking agent with or without the condensation catalyst. This effect was also noted for the shelf-stability of dimedone-functional one-component RTV silicone rubber composition disclosed in the patent of DZIARK, et al, U.S. Pat. No. 4,395,507. However, the above patents do not appear to disclose that the self-bonding adhesion of their compositions was improved by the foregoing pre-reaction of the cross-linking agent with the condensation catalyst and the adhesion promoter.
Accordingly, it is one object of the present invention to provide for an alkoxy-functional one-component RTV silicone rubber composition with good self-bonding properties to polyacrylate plastics.
It is an additional object of the present invention to provide for an alkoxy-functional one-component RTV silicone rubber composition with good self-bonding properties to various substrates.
It is yet an additional object of the present invention to provide for an alkoxy-functional one-component RTV silicone rubber composition with an improved cure rate and shelf-stability and good self-bonding properties to polyacrylate plastics.
It is still an additional object of the present invention to provide a process for producing an alkoxy-functional one-component RTV silicone rubber composition with good self-bonding properties to polyacrylate plastics.
These and other objects of the present invention are accomplished by means of the disclosure set forth herein below.